Control circuits



Oct. 7, 1952 G. I TAWNEY 2,613,341

CONTROL CIRCUITS Filed Aug. 8. 1951 2 SHEETS--SHEET l G. L. TAWNEY CONTROL CIRCUITS Oct. 7, 1952 2 SHEETS-"SHEET 2 Filed Aug. 8, 1951 .Motor 2| `will therefore stop at the point ,Where yv'vindirig)22, i'1as Zerosignal supplied to it. A tthis `point motoi-Z I1 and controlled object I9 will be pos iti'oned infexact .,r'zorrespondence' with the f controlling member I4 and the signal from rotor I8 as is desired. y

AFor providing a simple typeof Yhighly useful damping for motor 2I, use is made of the direct current component of the 'tube currents, and the circuit is arranged to provide a desiredamount of' direct current component in the motor Winding. In Figure'l this is done by rectifier 38 connected in series with a. variable vresistance 39 across the winding 22.` The resistancel3i9 is formed by a fixed resistor 39a. inparallel with avariable resistor @9b to obtain sensitive adjustment control, andl is adjusted to provide the desired degree of damping.,- Rectifier 38 is poled so that it will not conduct'currentpowingthrough tubes 26 and 21, whichgcurrentk is fed entirely tok-the motorf winding 22. However, WhentheA tube 26 or 21cuts off, thevinduced,electrornotive forcein winding -22 is then ofthe proper'polarity to pass current through rectier 38. The ow of direct current .in winding 22 is still the same, however, so that' rectifier 38serves to maintain direct current flow in the kmotor winding even during the tube c utoff periods. .This direct current provides a magnetic eld drag on the armature of motor 2| `proportional to the armature velocity andthereby has the same effect as viscous damping.

Figure 4 illustrates a circuit similar to that of Figure 1, but adapted to produce an output speed linearlyproportional. to an input control voltage, independent of theamplier characteristic; In Fig. 4,fa control voltage is supplied to terminals 46, to which is connected a circuit VI identical with the circuit of Fig. l, and including tubes 2E and 21 and their `associated circuit elements. The output ofcircuit 5I .is coupled to motor winding 22, as in Fig,l.- In addition, mechanically coupled to the rnotor'ZI is a tachometer 4I f @f conventional type having an Voutput 42 at which is producedA an alternating voltage of an amplitude proportional to the speed of rotation ofmotor 2 I and lof the line frequency. The phase ofuthestachometer output is preferably chosen as cophasal with the control signal. This output Y is supplied over a resistor 43 to the input 46 to v the control circuit. Thus, the control signal.

which may be the output from a selsyn or may be any other signal, isvapplied to terminals 46, across which is an input resistor 41 to whose high potential end is applied the feedback signal from l total-input to circuit 5I is designated asu; and

theratio of the feedback voltage appearing at 41 totheoutput speed is designated by B, thenin accordance with well known feedback circuit theory, the overall gain orratio of output speed,

to theinput control signal at 46 is given-by ..8 By making uB much larger than unity, this becomes,

'But 1'3" fa' characteristic of the tachometer alone, and s uch-tachometers `are available which arel accuratelyjlinea'r inV their speed-output characteristics. lHence the overall gain, oroutput speed'vsririputcontrolvoltage is made linear by `depending solely on the-tachometer for linearity, -andby eliminating the circuit as a, distorting factor.

`Sincethe speed-of the motor is thus linearly proportional tothe control signal, it will be apparentth'at the angle through which the motor turns is thus proportional to the time integral of Vthec'zontrol'signal, and thesystem of Fig. 4 can bejused za an integrating means.

j Itfwilllb understood that the system of Fig. 4

"canI also beusedto positionthe motor in correspondencejwithjtheecontrol signal, by providing repeat-back meansforreducing the control sig- -n'al as the motor turns, until a stable condition is reached with the control signal reduced to 'zero" One example of such a meansV is shown kin'gFig. Vl, ,although many' others are also known. `Ir'iisiich case the tachometer aids in preventing hunting or over-shooting.

, Fig. 5 shows a further circuit, here using series degenerative feedback from tachometer 4I. In thisc'ase,connected across control signal input terminals `46 aretwo resistors 48 and 49 in series. The' control circuitSI is coupled across resistor 48, while the. feedback signal is placed in series ftherewith 'by beingcoupled across resistor 49.

Otherwise Fig. 5 is the same as Fig. 4.

While thep'resent invention has been described yillustratively 'with respect to a control signal derived from a'selsyn system,.it`wil1 be understoodjtha'tiit is not limited thereto, but may be Vused 'Withjany source'. of 4alternating control signal 'of xed, eversible phase and variable mag- "1 -Since other apparently widely differing embodiments/of the invention are' possible withcu't departingfrom the spirit thereof, the above description is to be considered as illustrative only,

f and is nottobef'construed as limiting the invention which is defined solely by ythe appended clalllsf."4

A jWhatis cla med as` the invention is:

i l'.` A control circuit for actuating a two-phase motor"having' "a pair of windings in correspond'enc'e with a reversible-phase variable magnitude" alternating control signal, comprising la 'pair 'of'gasfdischarge tubes each having an ano'deacathode and ya control grid, the cathodes being interconnected,l a source of fixedmagnitude'y alternating' voltage, transformer means excited bys'a'id fixed voltage sourceand jhavinga 'rst secondary winding having a ycentertap, 'the outer terminals of said secondary winding being directly connected to said anodes to apply respectively .equal antiphasal voltages thereto, said transformer means having a'second secondary winding having a center tap, a phase-shifting network coupling the outer terg .ofr'itroi grids to applyequal'antiphasal bias voltf mi'nals offsaid second secondary Winding to said ages to said grids respectively leading said anode voltagesreversed by a phase angle of between l0 andvvQ electrical.. degrees and of a magnitude pr'jolducingfequal] currents throughl said tubes in .-thelfabsence' off'anyotherj grid voltages applied thereto, one winding of said motor being coupled between said iirst secondary winding center tap and the cathodes of said tubes, the other of said motor windings being excited from said fixed source substantially in phase quadrature to the excitation of said iirstk winding, and said control signal being adapted to be applied between said second secondary winding center tap and said cathodes with a phase angle leading one of said reversed anode voltages by less than the phase angle of said leading bias voltages relative to their reversed anode voltage.

2. A control circuit as in claim l further including means responsive to rotation of said motor for reducing the magnitude of said control signal whereby said motor assumes a position corresponding to the value of said control signal before reduction thereof. v

3. A control circuit for actuating a two-phase motor having a pair of windings in correspondence with a reversible-phase variable-magnitude alternating control signal, comprising a source of i'ixed alternating voltage coupled to one of said windings, a pair of gas discharge tubes each hav-v ing an anode and a control grid, transformer means excited by said source of xed alternating voltage and having a secondary winding with a center tap, the outside terminals of said secondary winding being coupled respectively to said control grids to provide bias voltages therefor, said reversible-phase variable-magnitude control signal being fed to said center tap, said transformer means having a second secondary winding with a center tap, the outside terminals of said second secondary winding being coupled respectively directly to said anodes, and the other winding of said motor being coupled to `said second center tap, whereby said two tubes are excited cophasally by said control signal and said motor is controlled by the sum of the currents through said tubes.

4. A control circuit as in claim 3, further including means comprising a phase-shifting network for causing each of said bias voltages to lead its respective anode voltage reversed by respective phase angles producing equal currents through said tubes in the absence of said control signal.

5. A control circuit as in claim 4 wherein said control signal has a phase-angle leading one of said reversed anode voltages by between zero degree and a value less than the lead angles of said bias voltages.

6. A motor control circuit, comprising a twophase motor having a pair of windings, one of said windings having xed excitation, a pair of gas discharge tubes having input and output electrodes, means exciting said input electrodes cophasally with a control signal, means exciting said same input electrodes anti-phasally by biasing voltages, means exciting said output electrodes anti-phasally, the other of said windings being coupled to said tubes in a parallel circuit arrangement to be excited by the sum of the currents in said tubes, said bias voltages having phases respectively leading said output electrode voltages reversed, said control signal having a phase leading one of said reversed output electrode voltages, and being of reversible-phase and variable magnitude.

7. A control circuit for actuating a motor having a variably excitable winding in correspondence with a reversible-phase variable-magnetude control signal, comprising a pair of gas discharge devices having input electrodes and output electrodes, means for exciting said output electrodes l with respectively equal fixed antiphasal alternating voltages, means for exciting said input electrodes byv respectively equal xed antiphasal bias voltages adapted to produce equal currents through said gas discharge tubes having fundamental frequency alternating components of opposite phase, means coupling said motor winding to said tubes to be excited by the sum of said current components through said tubes, and means for exciting said same input electrodes cophasally by said control signal, said control signal being phase-displaced with respect to one of said anode voltages.

8. A control circuit for a two-phase motor having a pair of windingscomprising a source of alternating voltage coupled to one of said windings,l a pair of gas discharge tubes each having an anode and a grid, a transformer having a primary winding excited from said source and a secondary winding having a center tap, said anodes being directly coupled to respective ends of said secondary winding, and said second motor winding being coupled to said center tap to be excited by the sum of the currents through said tubes, means for applying equal alternating bias voltages anti-phasally to said grids, and means for applying a control signal cophasally to said same grids.

GERELD L. TAWNEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,438,417 Russell Mar. 23, 1948 2,519,043 Greenwood et al. Aug. 15, 1950 2,545,223 Briggs n Mar. 13, 1951 OTHER REFERENCES Theory of Servomechanisms, -by James, Nichols and Phillips, McGraw Hill Book Co. Inc., 1947, page 208, paragraphs 1 and 2.

Publication, Electronic Industries, June 1948, pages 12 and 13. 

